Retirement Plans (Summary Of The Fair Values Of Pension Plan Investments According To The Fair Value Hierarchy And The Weighted Average Allocations) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guaranteed Deposit Account [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	$ 5	$ 12
Guaranteed Deposit Account [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	5	12	$ 9
Guaranteed Deposit Account [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	5	12
Limited Liability Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments		4
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	0	10
Common Stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	0	10
Common Stock [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments		15
Debt Investments [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	0	0
Debt Investments [Member] | Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	0	0
Debt Investments [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan investments	$ 166	$ 116